Method of forming integral fins on tubing



' May z3, 195o w; P. HILL METHOD 0F FORMING INTEGRAL FINS ON TUBING s sheets-sheet 1 Filed Oct. 1. 1945 WALTER P. HILL WML ATTORNEYS May 23 1950 w. P. HILL 2,508,517`

METHOD 0F FORMING INTEGRAL FINS 0N TUBING Filed Oct. 1'. 1945 3 Sheets-Sheet 2 FIG2.

INVENTR.

WALTER amm.

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ATTORNE/YS May 23, 1950 w. P. HILL METHOD 0F FORMING INTEGRAL FINS ON TUBING 3 Sheets-Sheet' 3 Filed Oct. 1. 1945 INVENTOR.l

WALTER P. HILL Y www ATTORN EYS asoasrr method for iinning tubing is the elemination of axial compression of the iin during the development of the same. To accomplish this the pressure which may be applied to the tube by one or more forming rolls is directed substantially radially inward and has no component directed axiallytowards the nn during its development. However, this radially inward pressure will produce a displacement of material which can flow substantially only in an axial direction while beneath the displacing surface but will be extruded radially outward at a point beyond said surface. Such extrusion is due to the combination of the axially directed pressure on the displaced material and the reaction of the body of'the tube against elongation thereof resulting in radial outward deflection. If the tube is confined so as to permit extrusion only through the root of the iin, then the entire fin will be developed from radially outwardly directed extruded material. In orderl however, to fashion the n to the desired cross sectional contour, the extruded material must be coniined between axially spaced surfaces of corresponding contour. As these surfaces are in xed relation to each other, they cannot axially compress the material therebetween but only direct it radially.

I have diagrammatically illustrated one form of the apparatus for producing finned tubing and more specifically for forming improved helical ns thereon. As shown in Figs. 1 and 2, A is a suitable frame including a pair of spaced paral- Y lelly arranged heads B and B' having bearings therein for rocker members C, C' and C3 extending therebetween and equispaced from each other. Each of these rocker members has eccentrically Journaled therein an arbor D for carrying a forming roll E.` The rocker members are connected to each other through the medium of radially outwardly extending arms C3 and connected links C4 so that when one of said members is rocked a similar rocking movement will be imparted to each of the others. Thus, the arbors D and rolls E may be simultaneously moved radii ally towards or from a central axis therebetween which is the axis of the tube to be finned. Each of the rolls E has a series of annular peripheral portions E', E. E3, E4, E5 separated from each other by grooves F, F', F, F3- which are slightly tapered in an inward direction. The portion E is substantially V-shaped in cross section with a radius curve at its outer end and is adapted to press a groove in the outer portion of the tube wall which extends helically thereabout (as hereinafter described). The portion E2, E3 and`E4 have their peripheral surfaces substantially straight in an axial direction but at a slight angle to the axis of the work. These surfaces are also progressively slightly increased-in width axially with a corresponding progressive decrease in the width of the grooves therebetween. The portion E5 has a peripheral face of still greater width which is parallel to the axis of the tube. It

` is to be understood that the axis of the rolls and the arbors carrying the same are at an angle to the axis of the work tube so that the portions E', E2, etc. are at the desired helix angle. Thus, while rolling about the -work tube in intersecting 'contact therewith, the portion E' will advance said tube axially and the portions E2 E3, E4 and E5 will successively traverse substantially the same helical path radially inwardly depressing the outer portion of the wall of the tube. The face of the portion lil'v adjacent to the groove F is substantially perpendicular to the axis of the work tube andwill. therefore, compel the axial advancement of said tubing and resist any stress tending to move the same in the opposite direction. The material displaced by the portions E. E3 and E4 will be forced to ilow axially therebe neath until in registration with the grooves which permit radial outward extrusion into said grooves. However, as these portions are progressively slightly increased in width, they will overlap portions of the tube wall not previously depressed and will force these radially inward. Thus, the width of the iinal groove FU and the extruded material therein will be less than that of the first groove but the pressure exerted on the material during its displacement will always be radially inwardly directed without exerting anyv axial lcompression of the extruded material in the groove. The work tube G while operated upon by the rolls is supported by a mandrel I which extends beneath the portions E', E2, E3, E* and E5. T-his mandrel is anchored at a remote point (not shown) and is of suiiicient length to receive the tube which is operated upon. However, at the operating point both mandrel and tube are floating with respect to the rolls engaging the same. 'I'he finned tube resulting from this process willhave the fins thereof of substantially uniform texture and -substantially free from work hardening on the surface portions thereof. Also, the peripheral edge of the iin will be convex in cross sectional contour, whereas the peripheral contour of the tips of ns produced by axial compression is concave and is subject to the development of cracks which may extend inward to the tube. Thus, the physical characteristics of the product are greatly improved.

If it is .desired to produce a nned tube having an unnned end portion of at least as great a diameter as the peripheral diameter of the fins, the original tube is preferably of this larger diameter. The rolls E are then provided with conical portions E which, first, come in contact with the tube while it is axially advanced and will reduce its diameter in advance of contact with the roll portion E'. Each of the succeeding portions will perform a further reduction in the diameter of the tube until limited by the mandrel I. The material displaced in this progressive decrease in diameter of the tube will be forced axially so that the portion of the tube on which the fins are developed will be increased in length. There will also be a change in helix angle in the rolling of the tube by the last section E5, the peripheral face of which is parallel to the axis of the tube so that the inwardly displaced material will elongate the tube between adjacent convolutions ofthe fin. In the completed structure the wall thickness of the finned portion of the tube will be considerably -reduced over that of the original tube, while the uniinned end portion will remain at the original diameter and wall thickness with the metal thereof in its original soft unwork-hardened condition.

The nned tubing produced by my improved method may have the fins thereof of any desired height in comparison with the diameter of the original tube. In the lproduct shown in connection with Fig. 3. the ,ns G are no greater in height than the original diameter of the tube G. On the other hand, in the product shown in Fig. 5 the ns H' are of considerably greater diameter than that of the original tube H.

comprises subjecting a. length of tubing to a circumferential rolling pressure applied in a radially inward direction on axially spaced helically aligned peripheral portions of progressively increasing axial extent and spaced apart progressively decreasing distances, extruding material from the tubing wall in a radially outward direction between the axially spaced peripher a l portions by the radially outward opposing force resulting from the radially inward rolling pressure applied to the wall of the tubing, and at the same time primarily guiding the extruded material to form a helically extending 1in.

2. The method of forming a length of tubing with an integral helically extending fin which comprises applying a circumferential rolling pressure to a length of tubing in a generally radiallyinward direction against axially spaced substantially helically aligned peripheral portions, and transmitting the radiallyinwardly directed pressure into a primary resultant pressure acting in a generally radially outward direction to displace material from the wall of the tubing radially outwardly between the axially spaced peripheral portions to form a helically extending n.

3. The method set forth in claim 2 in which the length of tubing is reduced in diameter and elongated in the direction of advancement of the tube by the application of the rolling pressure on the wall of tubing.

4. The method of forming from tubular stock a length of tubing with an integral helically extending iin and with an unflnned portion having a diameter at least as great as the diameter of the iin and approximating the diameter -of the stock, comprising applying/a circumferential rolling pressure to the length of tubular stock in a radially inward direction against axially spaced helically aligned peripheral portions of progressively increasing axial extent, transmitting the radially inwardly directed pressure into a primary resultant pressure acting in a generally radially outward direction to displace material from the wall of the tubular stock radially outwardly. between the axially spaced peripheral portions to form a helically extending iin, reducing the stock by the pressure of the fin rolling operation an amount approximating the height of the tin, and forming a cylindrical uninned portion of the length of tubing by relieving the fin rolling pressure.

5. The method of forming a length of tubing with an integral helically extending fin which comprises initially reducing the diameter of the length of tubing by applying a circumferential rolling pressure on the wall of the tubing and thereafter further reducing the diameter of the tubing by applying a circumferential rolling pressure in a radially inward direction against axially spaced helically aligned peripheral portions ofl progressively increasing axial extent, and transmitting the radially inwardly directed pressure into a primary resultant pressure acting in a generally radially outward direction to displace material from the wall of the tubing radially outwardly between the axially spaced peripheral portions to form a helically extending iin on the reduced length of tubing.

' WALTER P. HILL.

REFERENCES CITED The following references are of record in the tile oi.' this patent:

UNITED STATES PATENTS 

